Inside an application: Transducer aids pressure test

By Control Engineering Staff

02/22/2007

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Heat Transfer Products uses the Setra Model 201 to perform a pressure decay test during production of its Munchkin water heater. During this phase, the Munchin is tested to ensure that the water is heated to the proper temperature.

When Steve Asselin joined Heat Transfer Products of East Freetown, MA, as a project manager and specialist in automated test measurement, his initial assignment was to design a production line for the company's Munchkin line of water heaters. Since 1973, the company has been one of the Northeast's leading manufacturers of water tanks and water heating appliances for residential, commercial and light industrial use. The Munchkin line is one of the company's most popular product lines. The line consists of ultra high efficiency (92%) residential and commercial stainless steel heaters, all of which are compact in design, modular in construction, and quiet in operation.

Asselin knew that the most important aspect of designing the new production line would be designing the testing stage during which each boiler would be checked for its ability to literally perform under pressure. Asselin had worked with Setra Systems for more than 15 years, so called them to get the test measurement devices he needed for this testing phase.

"Previously," Asselin said, "I was involved in creating test machinery mostly for the manufacture of automotive components." He liked Setra for reliability, accuracy, and value. "So when I started working at Heat Transfer Products, without hesitation I called my Setra contact, Paul Richards."

Setra Systems of Boxborough, MA, is a leading designer, developer and manufacturer of electronic instrumentation for measuring pressure, acceleration and weight. Asselin says also he likes that Setra manufactures in the U.S., and is the only New England-based manufacturer with "an affordable sensor that can accurately measure very low gas pressure." He learned of Setra Model 201 pressure transducer, which was a prototype at that time.

Asselin set up two testing lines for the Munchkin boilers. The pressure transducer would come into play during the boiler firing rate test, the testing phase whereby the boiler is tested to make sure the boiler is firing at its designed rate. This test ensures that the appliance produces the amount of heat appropriate to its rating.

During Heat Transfer's boiler firing rate test, water from a 2,400 gal tank is pumped through the boiler under test. The boiler is then lit. As the boiler heats up, the gas flow into the boiler as well as other parameters are measured to determine the firing rate of the boiler. To accurately determine the gas flow rate, the pressure of the gas flowing into the boiler is measured. The Model 201 features an Inconel diaphragm and an insulated electrode, which forms a variable capacitor. As the sensor pressure increases or decreases, the capacitance changes. This change in capacitance is detected and converted to a fully conditioned linear current output signal.

"We have two shifts of technicians testing boilers," explains Asselin. "It takes several minutes to fully test each boiler. After each Munchkin is tested, it then proceeds down the assembly line to get cleaned up, stickers applied, boxed and palletized."

Asselin has accomplished his mission, establishing a new production line which incorporates an extremely efficient and reliable testing phase. Now that the pressure is off, figuratively speaking, Asselin is already working on future testing projects.

"Next spring we will be introducing a line of new high-output gas-fired wire tanks," Asselin says, adding that he's likely to consider pressure transducers that previously have performed well.